JPH05176216A - Lens distortion correcting system - Google Patents

Abstract

PURPOSE:To reduce the capacity of an address correction table in a lens distortion correction system in which a barrel lens distortion generated in a picture picked up by a wide angle lens is corrected by using the address correction table. CONSTITUTION:The system is provided with an address correction table 5 which relates a pattern address before distortion correction to a pattern address after distortion correction within an area divided at least in one direction in a horizontal direction and a vertical direction through the center of a screen and the address correction table 5 is used repetitively also for the address correction of other area of one screen. A lens distortion included in a picture obtained by a lens system is corrected to improve the visuality of a picture, and the capacity of the address correction table for lens distortion correction is reduced to 1/2 or 1/4, thereby reducing the cost.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a lens distortion correction method for correcting the geometric distortion of an input image generated by a lens system. It is suitable for use as a TV intercom that allows you to check the monitor in a house by shooting with a TV camera.

[0002]

2. Description of the Related Art A conventional TV intercom has an image pickup range of about 60 degrees in horizontal angle and about 45 degrees in vertical angle. There was a drawback that you couldn't see it. Therefore, it is conceivable to widen the image capturing range by setting the lens of the television camera to a wide angle, but in that case, there is a drawback that barrel-shaped lens distortion occurs due to the wide-angle lens and the screen becomes difficult to see. Generally, the geometric distortion of the input image caused by the lens system is not so noticeable to the human eye except for the wide-angle lens, and the lens distortion is a problem mainly in the case of the super wide-angle lens or the fisheye lens. It was As a means for correcting this kind of lens distortion, it is considered that an address correction table in which addresses before and after correction are associated with each other is prepared in advance, and the distortion is corrected by converting the pixel address according to this table. However, in general, the address conversion table needs to have distortion correction values for all points on the screen. For example, if the screen size is 512 × 512 pixels, an 18-bit address is required, and the memory for storing the address correction table is large. This increases the capacity and increases the cost.

[0003]

SUMMARY OF THE INVENTION The present invention has been made in view of the above points, and an object of the present invention is to correct barrel lens distortion occurring in an image picked up by a wide-angle lens into an address correction table. In the lens distortion correction method in which the correction is performed using, the capacity of the address correction table is reduced.

[0004]

FIG. 1 shows the basic configuration of the present invention. The input image signal is input to the sync signal separation means 1 and the A / D conversion means 2. The sync signal separating means 1 extracts both horizontal and vertical sync signals from the image signal. The other circuits operate in synchronization with this synchronization signal.
Further, the sync signal separation means 1 generates a pixel sampling clock synchronized with the sync signal. This clock is
It is used for sampling pixels in the A / D conversion means 2. The address generation means 3 counts the pixel sampling clocks and outputs the horizontal address (X
Address), and the horizontal synchronizing signal is counted to generate a vertical address (Y address). The X and Y addresses are input to the address conversion means 4, and the converted address x,
Output y. The converted addresses x and y are then input to the address correction table 5. The address correction table 5 outputs address correction values ΔX and ΔY indicating how many pixels are to be moved from the pixel in the X and Y directions in accordance with each pixel of the converted addresses x and y. The X and Y addresses from the address generation means 3 and the address correction values ΔX and ΔY from the address correction table 5 are added in the address correction means 6 to obtain the corrected addresses X + ΔX, Y +.
It becomes ΔY and is input as the address of the frame memory 7. The address correction table 5 is created in advance for each lens. The address correction table associates the address before correction and the address after correction in order to make the coordinate system of the image before correction including distortion into the coordinate system of the image without distortion. The correspondence between the addresses before and after the correction can be approximated by a general polynomial when the distortion changes smoothly, and therefore an appropriate polynomial is obtained and calculated.

On the other hand, the image signal is converted into digital image data in the A / D conversion means 2 by the pixel sampling clock. This digital image data is input to the dual port frame memory 7 and stored in the location designated by the correction addresses X + ΔX and Y + ΔY. A frame memory means generally called a dual port has two asynchronous ports, one of which is a random accessible port and the other of which is serially accessed in units of rows. The random access port is used for writing with the correction addresses X + ΔX and Y + ΔY. While writing while making this correction, at the same time, an image is read from the asynchronous serial port in accordance with the X and Y addresses created by the address generating means 3. The read image data is converted into an analog image signal by the D / A converting means 8, the synchronizing signal is mixed by the synchronizing signal mixing means 9 and displayed on the monitor television.

In the above description, the address correction processing is performed at the time of writing to the frame memory 7, but conversely, the writing may be performed serially and the reading may be performed while the address correction is performed from the random port. By using a dual port frame memory having such a serial port and a random port, lens distortion can be corrected at the video rate.

[0007]

The operation of the present invention will be described below with reference to FIG. As shown in FIG. 3, the barrel-shaped distortion caused by the wide-angle lens has a property that the distortion increases as the distance from the center of the screen increases, and the barrel-shaped distortion is displaced from the correct position without distortion toward the center of the screen. To correct this, conversely, if the pixel is moved in a direction to drive it out of the screen, the distortion is equivalently corrected. Of course, the image quality of the correction part will be degraded even if the image that is extremely distorted like a fish-eye lens is forcibly corrected, but if the distortion is not so great, you can restore the curved straight line to its original state. It is possible. In this case, it is naturally possible to perform more appropriate correction by correcting the pixel movement in the horizontal direction (X direction) and the vertical direction (Y direction). Specifically, address correction data is written in advance in the address correction table according to the distortion characteristics of the lens to be used. That is, a certain point (X, Y)
If the coordinates after the distortion correction are (X ', Y'), the output address when the point (X, Y) is input to this address correction table is (X ', Y').

In order to have an address correction table for the entire screen, as described above, a very large capacity memory is required, which is expensive. Therefore, in the present invention, a specific address conversion is performed and a table is created. The memory capacity is reduced. That is, since the lens distortion characteristic generally has a point-symmetrical characteristic with the center of the screen as the origin, the address correction process may be performed in a point-symmetrical manner. Therefore, even if the address correction table for the entire screen is not provided, it is possible to perform address correction for the entire screen by repeatedly using the address correction table for the 1/2 or 1/4 area. However, for this purpose, it is necessary to change the access direction of the address correction table.

Now, let us consider a case where an address correction table having a capacity of ¼ of one screen is used. FIG. 4 shows an example of an address correction table having a capacity of 1/4, which is obtained by dividing the screen vertically into two parts. In this example, as shown in the figure, in the upper left part of the screen, horizontal access is performed from left to right and vertical access is performed from top to bottom as indicated by an arrow. Further, in the upper right part of the screen, horizontal access is performed from right to left and vertical access is performed from top to bottom as indicated by an arrow. Next, in the lower left part of the screen, horizontal access is performed from left to right and vertical access is performed from bottom to top as indicated by the arrow. Further, in the lower right part of the screen, horizontal access is performed from right to left and vertical access is performed from bottom to top as indicated by an arrow. Then, in the address correction table, the relative displacement Δ from the input address X, Y
By storing X and ΔY, the capacity of the table can be reduced to 1/4 as compared with the case where the address correction table for the entire screen is stored. Further, the capacity of the address correction table can be reduced by storing the output addresses X + ΔX and Y + ΔY as relative values instead of storing them as absolute values.

Specifically, X, which is generated by the address generation means,
The address conversion means at the next stage performs the above address conversion on the Y address to generate an x, y address. In the case where the screen size is 512 × 512 pixels, for example, considering the first one horizontal line, when the address generation unit sequentially outputs the X and Y addresses from (1,1) to (512,1), the address conversion unit. Received this (1,
1) to (256, 1) are output as they are, and (25
On the contrary, from 7, 1), decrement the x address,
The addresses from (256, 1) to (1, 1) are output.
That is, the horizontal address x after conversion is x = X when 1 ≦ X ≦ 256, and the horizontal address x after conversion is x = 513-X when 257 ≦ X ≦ 512. Next, regarding the Y address conversion of the address conversion means, 1 ≦ Y
When ≦ 256, the converted vertical address y is y = Y, and when 257 ≦ Y ≦ 512, the converted vertical address y is y = 513-Y. The address correction table is accessed by the converted addresses x and y. In the address correction table, displacement data Δ indicating how many pixels X and Y are moved relative to the input address.
X, ΔY is output, and the original address X, Y is added to the displacement data ΔX, ΔY by the address correction means to obtain the corrected address X + ΔX, Y + ΔY, and the image data is written to that address in the frame memory. is there.

However, when the displacement data ΔX and ΔY are added to the original addresses X and Y in the address correcting means, the displacement data ΔX and ΔY are respectively given a minus sign in the upper left portion of the screen, that is, subtraction is performed, In the lower right part of the screen, it is necessary to add displacement data ΔX and ΔY with a sign of + respectively. Similarly, in the upper right part of the screen, the displacement data Δ
It is necessary to add a sign of + to X and a sign of − to the displacement data ΔY, and add the sign of − to the displacement data ΔX and a sign of + to the displacement data ΔY in the lower left part of the screen. It is necessary to add and add. In this way, it is necessary to switch the signs of the displacement data ΔX and ΔY because the distortion characteristic of the lens is always displaced from the correct position toward the center of the screen, so the distortion correction is performed in the opposite direction, that is, This is because it needs to be displaced toward the outside of the screen. Therefore, the address correction means has a flag indicating in which area of the area the current address is divided into four, and accordingly, the displacement data ΔX and ΔY to be added to the original addresses X and Y, respectively. It is necessary to switch the sign.

As described above, the address correction table having the capacity of 1/4 of the entire screen can be used four times to perform the correction of the entire screen. It can be reduced to 1/4.

It should be noted that the lens distortion correction method of the present invention can obviously obtain the same effect when an address correction table having a 1/2 capacity obtained by dividing a screen vertically or horizontally is used. Is.

[0014]

FIG. 2 shows an embodiment of the present invention. In the present embodiment, for example, in a general house or an apartment house, a lens distortion having a configuration shown in FIG. The correction means is used. This television intercom includes a television camera 10 equipped with a wide-angle lens and a slave 12 having a microphone 11 for collecting the voice of a visitor, a signal transmission system 13 for transmitting an image signal and an audio signal from the slave 12, and a slave. An image signal sent from the child device 12 by using a wide-angle lens, which includes a monitor TV 14 that displays an image from the device 12 and a parent device 16 that has a speaker 15 that outputs the sound from the child device 12. 3 contains barrel-shaped lens distortion as shown in FIG. 3, but by correcting this with the lens distortion correction means 17 having the configuration shown in FIG. 1, a high-quality image with little distortion is monitored. be able to. For example, it is possible to correct the shape of an object, such as the face of a visitor, which is about 50 cm away from the television camera, to make it easier to see.

[0015]

According to the present invention, there is an effect that the lens distortion included in the image obtained by the lens system can be corrected and the visibility of the image can be improved. The address correction table capacity is 1 /
The cost can be reduced to 2 or 1/4, and the cost can be reduced.

[Brief description of drawings]

FIG. 1 is a block diagram showing a basic configuration of the present invention.

FIG. 2 is a block diagram showing a configuration of an exemplary embodiment of the present invention.

FIG. 3 is an explanatory diagram showing a state of lens distortion caused by a wide-angle lens.

FIG. 4 is an explanatory diagram showing access directions of an address correction table used in the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 sync signal separation means 2 A / D conversion means 3 address generation means 4 address conversion means 5 address correction table 6 address correction means 7 frame memory 8 D / A conversion means 9 sync signal mixing means

Claims (3)

[Claims] 1. A sync signal separating means for separating a sync signal from an image signal of a television camera using a lens system having a point-symmetrical distortion about an optical axis, and an A / D converting means for digitizing the image signal. And an address generating means for generating a screen address from the synchronizing signal, and a screen address before distortion correction and a screen address after distortion correction only in a region divided in at least one of the horizontal direction and the vertical direction through the center of the screen. An address correction table that associates with the address correction unit that converts the screen address generated by the address generation unit into an address within the area of the address correction table; and an image at the screen address before distortion correction based on the output of the address correction table. The frame memory that writes the digital value of the signal to the screen address after distortion correction, and the frame A lens comprising D / A conversion means for D / A converting the digital value read from the frame memory and synchronization signal mixing means for mixing a synchronization signal with the output of the D / A conversion means. Distortion correction method. 2. The address correction table stores a difference between a screen address before distortion correction and a screen address after distortion correction as a relative displacement, and the screen address before distortion correction is stored in a plurality of divided areas. 2. The lens distortion correction method according to claim 1, further comprising address correction means for adding a relative displacement having a different sign depending on which region it belongs to, to a screen address before distortion correction. 3. A slave unit having a television camera equipped with a wide-angle lens and a microphone for collecting a voice of a visitor.
Lens distortion correction in a TV intercom consisting of a signal transmission system that transmits image signals and audio signals from the slave unit, a monitor TV that displays images from the slave unit, and a master unit that has a speaker that outputs the sound from the slave unit. The lens distortion correction method according to claim 1 or 2, wherein the means is provided in the master device.